Advanced Materials

Multimodal atomic force microscopy (AFM) was used to map charge transfer properties in correlation to the molecular superstructure of poly(ethyldioxythiophene)–poly(styrenesulfonic acid) (see Figure). The lamellar domains of the polymer blend are indicated by phase shifts. Efficient charge injection occurs when lamellar edges of the superstructure are exposed to a conductive AFM probe. Efficiency of charge injection at polymer–electrode interfaces could be enhanced by controlling lamellar orientation.

Laminar-flow microfabrication is shown to produce complex micrometer-resolved polyelectrolyte micropatterns at ambient conditions (see Figure). This simple deposition procedure shows great versatility, with the capacity to fabricate micropatterns containing unstable and sensitive biological objects on the surface of any appropriate substrate.

Stretchable electronic circuits have been microfabricated using tortuous gold wires embedded in silicone elastomer. With appropriate geometric parameters, the wires could elongate by more than 50 % while maintaining stable conductivity (see Figure). This technology represents a key development towards conductive fabrics, flexible displays, and other applications that require electronics to withstand unprecedented degrees of stress and vibration.

Material storage in the inner spaces of nanocarbon materials is visualized for the first time. It is shown that creating paths of a specific size to the inner space (see Figure) is indispensable for material storage in carbon nanopores, and that the adsorption rate for fullerene molecules is largely dependent on the nanoscale curvature of the graphitic planes composing the nanospaces.

CNT/crystalline Fe nanocomposites (see Figure) have excellent microwave-absorption characteristics. This absorption property is shown to result from the confinement of crystalline Fe in carbon nanoshells, deriving mainly from magnetic rather than electric effects—the complex permittivity and permeability depend both on the shape and phase of the CNT/Fe nanocapsulates.

A new method for direct patterning of metal surfaces with sub-50 nm resolution based on molecular films is described (see Figure). Thermal vapor deposition of different metals on chemically surface-modified nanostructured silicon or metallic masters allows direct pattern transfer and easy film detachment. Patterned metallic surfaces are also used as platforms to grow nanostructured hybrid materials by controlled chemical reactions.

An easy, cheap, high-throughput way to generate metallic wire arrays by patterned electrodeposition is reported. Copper is electrodeposited on the surface of a regularly striped Langmuir–Blodgett film, forming an array of submicrometer-wide wires with homogeneous width (see Figure). Width and separation of the wires can be tuned by the template.

Micrometer-scale patterns of blue photoluminescing CdS nanoparticles can be produced by microcontact printing on a hydroxyl-terminated silicon wafer surface (see Figure). The CdS nanoparticles were synthesized with amine-terminated generation eight dendrimers as stabilizers. The resulting CdS/dendrimer composite is directly printable due to hydrogen bonds between dendrimer and surface.

The preparation of ordered arrays of metal hollow spheres via colloidal crystal templating is reported. A seeded growth technique for metal coatings on isolated colloids in solution and a confined template-directed synthesis method for metal patterning were combined. The polymer colloidal crystal template was prepared and kept stable using a microchannel. 2D and 3D ordered microstructures of silver hollow spheres were obtained (see Figure).

In nanotube-based electronics, Al₂O₃ nanotubes will play a very important role. A method is reported that yields nanotubes with controllable, uniform wall thickness. The Figure represents the stage of the synthesis in which ZnO nanowires synthesized on a thick polycrystalline ZnO layer on a Si substrate have been coated with Al₂O₃ and the ZnO partially etched away. When the etching is complete, Al₂O₃ nanotubes remain.

GaN nanocrystals (see Figure) of hexagonal structure and varying diameters have been prepared by the reaction of hexamethyldisilazane (HMDS) with gallium cupferron or GaCl₃ under solvothermal conditions. The nanocrystals show a size-dependent photoluminescence band in the 260–320 nm region, characteristic of quantum confinement.

The fabrication of carbon nanotubes (CNTs) with controlled cross-sectional shapes is reported for the first time. Anodic porous alumina with triangular openings is used as a template for the chemical vapor deposition synthesis of the CNTs with triangular cross-sections (see Figure). The CNTs can be applied to the fabrication of nanoscale devices that require modified electronic characteristics.

Mononuclear Cu^I complexes with mixed ligands are used to fabricate green phosphorescent organic light-emitting diodes. The electroluminescence (EL) maximum at 524 nm coincides well with its photoluminescent (PL) spectrum in poly(methyl methacrylate) film (see Figure). A maximum current efficiency of 10.5 cd A^–1 at 105 cd m^–2 and a maximum brightness up to 1663 cd m^–2 are demonstrated.

Highly anisotropic TiO₂ nanostructures (see Figure) of several hundreds of nanometers in length were obtained by oriented assembly of preformed TiO₂ nanoparticles with typical diameters of 5 nm. The assembly is directed by a particularly small amount of a polydentate ligand with a low molecular weight, which binds selectively to specific crystal faces of the titania nanoparticles.

A simple criterion to identify potential phase-change materials is developed using density functional theory. These compounds rely on the switching between an amorphous and a crystalline state. Here it is demonstrated that suitable alloys have an average valence electron number larger than 4.1 and show p-electron bonding leading to a six-fold coordination, while materials with a smaller number of valence electrons favor sp³-bonding (see Figure).

Molecular-scale “glass” blowing of multi-wall carbon nanotubes into nanobulbs (see Figure) is achieved in a unique tube growth environment generated by the explosive decomposition of picric acid. Results indicate that carbon nanotubes have remarkable thermoplasticity and structural fluidity during their generation, and can be engineered into various shaped micro-vessels or devices.

The use of phosphorus as a co-catalyst enabling modification of the kinetic equilibrium between the elementary growth steps of multiwalled carbon nanotubes and induction of a mechanism of sequential catalytic growth is reported. The mechanism produces nanotube-based filaments periodically inserted with catalyst nanoparticles, which resemble nanoscale matches (see Figure).

A new approach to the ‘3D solar-cell concept’ is reported. Atomic layer chemical vapor deposition is employed to infiltrate CuInS₂ into the pores of nanostructured TiO₂. In this way it is possible to obtain a nanometer-scale interpenetrating network between n-type TiO₂ and p-type CuInS₂. Cells created this way show photovoltaic activity with a maximum monochromatic incident photon-to- current conversion efficiency of 80 %.

A polymer with a rigid, randomly contorted molecular structure (see Figure), incorporating fused rings connected by spiro-centres, may be precipitated or cast from solution to give microporous powders and membranes stable up to temperatures of 350 °C, with apparent surface areas > 600 m² g^–1. Organophilic membranes may be formed, as demonstrated by the separation of phenol from water by pervaporation.

Gold nanostructures—nanowires and nanosheets—are reported to have been prepared from the gold salt HAuCl₄ in a solid bulk phase of a block copolymer. The Figure shows a SEM image of nanosheets formed by thermal reduction at 70 °C. If water is included in the initial mixture and the reduction occurs by UV irradiation, predominantly nanowires are produced. Reasons for this distinction are discussed.